Experts say a steel pipe is at least partly to blame for halting a massive tunnel-boring machine beneath downtown Seattle. The state Department of Transportation said today (Friday) that an 8-inch-diameter pipe was discovered protruding through an opening in the machine's cutter-head. Officials say the pipe is a well casing installed by the department in 2002 to monitor groundwater. Chris Dixon is the Seattle Tunnel Partners Project Manager. “A cutter head won't line through and cut up steels. Very good with clay and sands and boulders and gravels but …not good with metal.” He said.